mixins.clj

;; Protocol defining output with external logic:

(defprotocol Outputter (output [self logic]))

;; Simple record:

(defrecord Person [name])

;; Two protocol definitions:

(deftype OutputterTrait [target] Outputter (output [self logic] (logic target)))
(deftype DummyTrait [] Outputter (output [self logic] (println "ignored external logic")))

;; Person instance:

(def joe (Person. "joe"))

;; Mixin function:

(defn mix [source mixins] (let [m (merge source mixins)] #(get m %1)))

;; Mixed joe:

(def mixed (mix joe {:outputter (OutputterTrait. joe) :dummy (DummyTrait)}))

;; Now using our mixed joe:

(output (mixed :outputter) #(println (:name %1)))
(output (mixed :dummy) #(println (:name %1)))